The present invention is related to the field of exposing (imaging) printing plates, and in particular, a clamping device for flexible plates that may have different thickness and/or format onto an imaging cylinder, e.g., for exposure in a computer-to-plate imaging device by light energy according to imaging data.
Flexographic plates are frequently exposed from computer data using computer-to-plate (CTP, C2P) imaging. Mounting such plates on a cylinder, e.g., the cylinder or drum of an external drum imaging device is recognized as a problem. For example, one method to mount a flexographic plate on a cylinder is to fix the plates with adhesive tape at the edges. More modern methods use a clamping bar, which clamps the top and bottom edge of a full-size flexographic plate onto the cylinder. The adhesive tape method is very time consuming and the second method using a clamping bar only works with full format plates. Since flexographic plate material is relatively expensive a modern method to mount partial plates on a full format cylinder are becoming more and more important.
An example of an external drum imaging device for which such a method and apparatus is applicable is the Esko-Graphics Cyrel Digital Imager (CDI) made by Esko-Graphics A/S, Ballerup, Denmark, the assignee of the present invention.
There is a need in the art for an economical easy-to-use method and apparatus to mount plates of different thickness and format directly onto the imaging cylinder.
In this description and in the claims, by a full-format plate is meant a plate that covers the whole imaging area of the cylinder. By a partial-format plate is meant a plate that covers part of the overall imaging area, such that several partial-format plates (also called plate segments) may be combined to cover the whole imaging area.
One prior art method is for a machine operator to manually mount a full-format plate or partial-format plates onto a cylinder with adhesive tape. Such a method is used, for example, by external drum imaging machines such as the ThermoFlex™ product line made by CREO Inc. of Burnaby, BC, Canada. However, to mount full-format or partial-format plates with adhesive tape is highly time consuming, the operator first mounts a first edge of the plate on the cylinder, fixes it with adhesive tape, turns the cylinder around so that the plate covers the cylinder, and then tapes all the rest of the edges of the plate.
Another prior art solution is for the machine operator to mount full-format plates—those that fully cover the circumference of a cylinder—with the use of a clamp, which is activated manually. An example of a device for so mounting full-format plates is a device used with an imaging drum, called EasyClamp™, made by Esko-Graphics A/S, Ballerup, Denmark, the assignee of the present invention. If partial-format plates are used, the machine operator first mounts partial-format plates onto the cylinder with the use of adhesive tape. The mounting by use of adhesive tape, as stated above, is time consuming.
Yet another prior art solution is for the machine operator to mount full-format plates—the case of the circumference of the cylinder being fully covered by the plate—using a terminal strip, which is activated manually. For mounting a plate, the terminal strip has to be opened manually, the plate has to be fixed under the terminal strip, the terminal strip has to be closed manually, the cylinder then has to be turned around, the terminal strip has to be opened manually again, the second plate edge has to be positioned under the terminal strip and then the terminal strip has to be closed manually. In all cases with the use of a terminal strip, the activation is done by manually by turning a key. This method is suggested, for example, in the HelioFlex® range of products made by HELL Gravure Systems GmbH of Kiel, Germany.
Note that as is the case with the Esko-Graphics EasyClamp™, the terminal strip is only for full-format plates. The machine operator mounts partial-format plates with the use of adhesive tape. The mounting by use of adhesive tape, as stated above, is time consuming.
There thus is a need in the art for a method and apparatus that improves the manual steps of opening and closing clamping devices or a terminal strip.
There further is a need in the art for an imaging cylinder such as a printing-plate-holding imaging cylinder that includes a plurality of clamping devices, positioned in a respective plurality of different axial positions, in a respective plurality of different circumferential positions, and/or in a respective plurality of both different axial and different circumferential positions, in order to avoid having to use adhesive tape to fix a partial-format plate to a imaging cylinder.
Thus both partial and full-format plates can be directly clamped at the end edges by the clamping device.
There is a need in the art for integrating a mechanism into an imaging cylinder to clamp and release flexible plates. There further is a need in the art for a clamping mechanism and clamping method that can work for a relatively large number of plate formats and thicknesses.
U.S. patent application Ser. No. 11/331,424 to inventors Koberg et al., titled METHOD AND APPARATUS TO CLAMP AND RELEASE FLEXIBLE PLATES ONTO AN IMAGING CYLINDER and filed on Jan. 12, 2006, describes a method and apparatus for fastening flexible plates onto an imaging cylinder, e.g. for digital flexo plates or rubber, e.g., elastomere plates, or conventional flexo plates. In one embodiment of that patent application, an imaging cylinder includes a clamping device, and the method includes placing end edges of a flexible plate between a clamping element of the clamping device and the outer surface of the cylinder. Springs are used to impart a force onto the placed plate towards the outer surface of the cylinder. An inflatable hose and springs are used to open a space between the clamping element and the outer surface to provide for mounting and unmounting plates. In one embodiment, opening the clamping device is activated by applying air pressure from a pump or external connection. In such a manner, the operator only has to press a button or a foot panel to open or close the clamping device. Another aspect of U.S. patent application Ser. No. 11/331,424 is that by using more clamping devices, placed axially and/or in the circumferential direction, the need for adhesive tape to fix partial format plates onto the cylinder might be avoided. Partial and full-format plates are thus directly clamped at the end edges by the clamping devices.
The U.S. patent application Ser. No. 11/331,424 clamping device(s) require(s) a source of air pressure.
There still is a need in the art for a simpler manually operated method for fastening flexible plates onto an imaging cylinder, and also for an apparatus for carrying this out.
There further is a need in the art for a manually operated method for fastening flexible plates onto an imaging cylinder that includes using independent adjacent manual clamps, one for a leading edge of a plate and the other for a trailing edge of a plate and also for an apparatus for carrying this out.
There further is a need in the art for a manually operated method for fastening flexible plates onto an imaging cylinder that can be placed at different positions on an imaging cylinder, e.g., in one or more different radial and/or different axial positions.